The present invention relates to a biodegradable invasive medical device, especially for tissue regeneration, which device comprises a biodegradable polymer, composed of a thermoplastic and/or thermosetting polymer, mixed with one or more solvents, which solvents are miscible with water and/or with any aqueous and/or aqueous alcoholic and/or alcohol-group-containing solution, and/or with physiological liquids, whether of a synthetic or natural type.
Polymers of this type are already known and are currently widely used for tissue regeneration and specifically for the regeneration of bony and ligamentous tissues in general, and in particular periodontal tissues in periodontal pockets.
For example, European Patent No. 0,484,387 describes a polymer of this type, in which the mixture of the thermoplastic polymer and the solvent is in liquid form, so that it can be applied by injection with a syringe fitted with a needle.
When the liquid mixture has been injected, the water or the physiological liquid acts to wash away the solvent, while the polymer, which is insoluble in water, forms a porous filling that can be penetrated by solvated proteins and salts, followed by the cells that will regenerate the tissues.
A notable disadvantage of the known biodegradable polymer is that the application as a liquid solution cannot be easily contained and confined to a given site, especially when the zone of application does not have any fixed boundaries. The liquid spreads in an uncontrolled manner, reaching positions or sites where its presence is undesirable.
U.S. Pat. No. 5,487,897 relates to a similar polymer in the form of a bag with a containing outside wall that is relatively hard but still mouldable, and which has the mixture of thermoplastic polymer and solvent in a substantially liquid state inside it. The aim of this object is to solve the problem of confining the use of the polymer in liquid form. On the one hand, this does ensure the containment of the core of the liquid in the bag, but on the other hand the formation of the bag, which also consists of a biodegradable polymer, requires a complicated process and cannot be done easily by medical personnel. There is no effective way of checking the success of the operation involved in the preparation of the bag, and the results are therefore far from being guaranteed, not to mention the manual skill needed, the loss of time, and the need to observe the times and conditions of the preparation.
Another disadvantage of the polymers according to the prior art described in the documents mentioned above is that the liquid and the bag containing it must be washed away completely by the physiological liquid in order to eliminate the solvent. The washing-away naturally starts at the outer surface of the implanted mass and then advances progressively towards the centre of the implant. Relatively long periods of time are therefore needed to ensure the washing-away of the whole volume of the implanted polymer and solvent solution, and hence the complete hardening of the polymer mass. In addition, the solidifying outer layers reduce the speed at which the physiological liquids penetrate the inside of the implanted polymer mass.